possible gcse failure: not able to eliminate redundant loads

[Sanjiv Kumar Gupta, Noida]

>> But surely it should be smart enough to know they don't alias?
>It depends on what it looks like at the RTL level.
the references of a[4] and a[1] appear as two pointer pseudos
which gcc can not determine that they have been computed with distinct
offsets from same base. Thus assumes aliasing.
I am implementing mod-k residue technique in GCC 
(described in "alias analysis of executable code", Debray98 et. al)
to fix this.
>> This is still a bug, possibly an important one for performance.

>Store motion can't handle this right now.
>It was built to handle a certain special case.
>Improve it so it does more.
>It's not broken, just not as good as it could be.

Store motion is currently disabled. see gcse.c line 910

/* Store motion disabled until it is fixed.  */
  if (0 && !optimize_size && flag_gcse_sm)
    store_motion ();

I don't know what's stopping this? I will try to find
related PRs and have a look into them.

--Sanjiv